Stereoscope



pr 8 1933; I H. F. KURTZ 1, 8

I STEREOSCOPE Original Filed Sept. 26, 1927 2 Sheets-Sheet 1 HENRY F. KURTZ INVENTOK A TTORNE V April 18, 1933. H. F. KURTZ 1,904,868

' STEREOSCOPE Original Filed Sept. 26. 1927 2 Shuts-Sheet 2 F L u G I)?- v R T 1 R HENRY F. KURTZ 4 INVENTOK ATTORNEY whereby true application Serial No. 222,161 led Patented Apr. 18, 1933 UNITED STATES PATENT OFFICE HENRY F. KURTZ, OF ROCHESTER, NEW YORK, ASSIGNOR TO BAUSCH & OPTICAL COMPANY, OF ROCHESTER, NEW YORK, A CORPORATION 01' NEW YORK s'rmmoscorn Original application illed September 26, 1927, Serial No. 222,161. Divided and this application filed Kay 19, 1980. Serial No. 453,530.

This invention relates to stereoscopic viewing devices and-more particularl it has reference to a device for stereoscoplcally recomposing X-ray stereograms which have been produced under certain conditions and accurate stereoscopy can be obtained. 4

This case is a division of m 00- ending S e tember 26, 1927.

One of the objects of the present invention are geometrically homologous to the condi tions under which the stereograms were produced. Another object is to provide a stereoscopic viewing device wherein objects under observation may be viewed at normalviewing distance from the observer. A further object is to provide a reflecting stereoscope with negative lenses whereby the-reflected images of the objects under observation will be imaged at a distance from the observer which is less than the distance from the stereoscope to the object. These and other objects and advantages reside in certain novel features of construction, arrangement and combination of parts as will hereinafter be more fully described and pointed out in the appended claims.

The usual practice in stereographic roentgenological diagnosis involves the production of a pair of X-ray negatives or stereograms by successively exposing two sensitized elements to a source of X-rays, the source being shifted a certain distance, very generally 2 inches, between the successive exposures. These negatives or stereograms are then placed ina stereoscopic viewing device and adjustments are ,made until some sort of semblance of fusion of the two images is obtained. Although this affords views having relief or stereoscopic efl'ects, such views do not accurately portray the subject in three dimensions, with the resulting eifect that serious errors are introduced when an attempt is made to determine the exact location of a foreign body or a pathological condition, for example. Since an operating surgeon is very often guided solely, by the fortable stereoscopic vision is dependent upon the proper observance and correlation o certain principles of vision.

Referring to the drawings:

Fig. 1 is a diagrammatic view illustrating my method of exposure.

ig. 2 is a diagrammatic view showing an incorrect viewing method in which convergence and accommodation are not harmonized.

' Fig. 3 is a diagrammatic view illustrating my improved method of viewing stereograms.

F i .4 is a diagrammatic view which shows a re ecting stereoscope adapted for viewing large stereograms and modified according to my present invention.

The general conditions necessary for accurate and comfortable stereoscopic vision are a harmony between accommodation and convergence and a recise, definite difi'erence in perspective etween the views presented to two'eyes.

Accommodation is the power of varying the focus ofthe eye to'bring divergent rays together on the retina and theamount 0 accommodationnecessarily varies for objects locatedat difi'erent distances. Convergence is the ability to direct the visual linesof the two eyes to a near point. If one looks at a distant object accommodation is relaxed and resulting recomposition is inaccurate and.

very uncomfortable. This result is invari ably produced when the usual methods of stereoscopicroentgenography' are employed.

Accommodation and conver ence are correspondlngly associated and or a given distance there is one degree of accommodation "and a corresponding single degree of concondition is dependent upon the fact that the The fulfillment of the conditions of har-' mony between accommodation and convergence and a difference in perspective between the views which is correct in aspect, but of any degree, is suflicient for the production of relief effects or plastique. However, in order that the degree of plastique shall'not be excessive'or insufiicient, that is, that the third dimension shall be precise, the fulfillment of a third condition is necessary. This degree of difference in perspective between the right and left views increases as the viewing distance decreases. The difference ata is therefore specific to given distance that distance. This, interpreted in terms of roentgenol-ogical stereoscopy means that negatives or stereograms taken at a given distance must be viewed at the same distance, or

under geometrically homologous conditions which can be secured by a properly designed viewing device. a

In order to'more clearly explain a describe -my invention, X-ray stereogras of the human chest-will be used by. way of illustration. It is obvious, however, that my invention is not limited to X-ray stereograms of the human chest, as it may be applied with equal effect and advantage to the roentgenological examinations of any object or objects.

In the usual practice of making X-ray stereograms ofthe human chest, the exposure distance, that is, the distance from the plane of the focal point or anode .of the X-ray tube to the sensitized element, is usually anywhere from 20 to inches. stereograms exposed at this distance are then usually viewed 1n a device having a viewing distance which varies from 27 to 36 inches. Such p ractices violate the aforementioned principles of accurate stereoscopic vision and one viewing such stereograms ofthe chest experiences discomfort, besides receiving an impression generally that the chest lacks depth to a marked degree.

The first requisite the development. of my improved method is the establishment of a normal viewing distance. This may be defined as that distance between the eyes and an object that results in maximum-plasticity consistent with comfort. The nearer, within reasonable limits, an object is to the eyes the more pronounced is the plasticity, that 'portional is, the impression of relief or third dimension becomes more pronounced as the distance diminishes. Experience shows that an object may be comfortably viewed at a distance of 15 inches, but that as the distance becomes less, vision becomes dilficult because of the severe accommodative'efl'ort. The average person with active accommodation sees comfortably at 10 inches, but allowing for variation in individuals, it is reasonable to assume 15 inches as a normal viewing distance. Al-

though I have used 15 inches as the normal viewing distance in this specification, it is for illustration only, and it is to be distinctly understood that I do not limit my invention to a normal viewing distance of 15 inches.

When a normal viewing distance has been established, the convergence angle is auto.- matically angle subtended by average interpupillary distance, namely, 2% inches, at normal view:

ing distance. Since 15 inches has been se; lected as normal viewing distance for purposes of illustration in this specification, the convergence angle of my illustration Wlll be the subtense of 2 inches at. a distance of 15 inches. The interpupillary distance of 2% inches is anaverage and is byway 6f illustration only, as my invention is not limited to an interpupillary distance of 2 inches. Y

In order to produce X-ray stereograms in accordance with my method, this would mean-that the X-ray tube would be positioned only 15 inches from the sensitized element and that the tube would be shifted only 2 inches between successive exposures. As it is obviously impossible to work at this distance, other expedients must be resorted to in 'order to obtain correct convergence condltlons 1n accordance with my 1nvent1on.

established, since it must be the Upon experiment, it was found that a distance of 45 inches from the anode of the X-ray' tube to the sensitized element is suitable. At this distance the entire chest of the larger subjects is projected upon a 14" x 17 film-when exposed with the necessary tube shift. In order to meet the convergence conditions required by my invention, it is necessary to shift the X-ray tube 7 inches between successive exposures when working at an exposure distance of 45'inches. The triangle represented by the subtense of 7 inches at 45 inches is mathematically proto the triangle represented by the subtense of 2 inches at 15 inches. Although I have used 45 inches distance, and 7 inches as a is by way of illustration only, and it is to be as an exposure tube shift, 1t-

understood that my invention can be equally well applied to other exposure distances and tube shifts;

Fig. 1 of the drawings illustrates my method of producing X-ray stereograms by successively exposing two sensitized elements to a source of X-rays, the X-ray tube being shifted between exposures. The anode of the X-ray tube, indicated at 10, is located at the full-line position for the exposure of the first negatives and is laterally shifted to the dotted line position for exposure of the sec sensitized element define a plane which is perpendicular to the sensitized element. An

lmaginary axial line 00' hes in this plane. The sensitized elements, which may be either plate or film, are indicated at 11 and 12. Although these-elements 11 and 12 are shown slightly spaced on Fig. 1, they are actually successively placed in the same plane when exposures are made, as will be readily understood by one skilled in the 71/ inches does not for each individuaLeye.

' axis line 00' art. a

If these films, after development, were replaced in this system in precisely the same posltions occupied during exposure, and if the right eye could be placed in the position occupied by the X-ray source for the exposure of the first film 11 and if the left 1 eye could be placed at the position occupied by the source for the exposure of the second film 12, a precise comfortable view would be received providing the right eye could view' only the negative 11 and the left eye only negative 12. This, however, is impossible because an interpupillary distance ofv exist and becausesuch an arrangement JWOllld not permit selectivity Fig. 2 illustrates a viewing arrangement which is designed to overcome these two difficulties. In this arrangement film 11, which was exposed when the X-ray source 19 was located in the full line position at the right in Fig. 1, is ofl'set to the left of the a distance FG which in this illustration is equal to 2 inches. The film 12, which was exposed when the source 10 was located at the dotted line position shown 1n Fig. 1, is offset to the right a distance GI-I which is equal to 2 inches in the illustration under consideration.

This arrangement allows vision under the correct convergence with an interpupillary distance of 2 inches between the eyes E, E. It is to be understood that these olfsetting movements involve translation only, with no rotation and it is to be further understood that the films 11 and 12 are very 'trated, the films 11f are adapted to reflect small so that the ofl'setting movements will completely separate the films. The amount v of offset of the films in any case is obtained by subtracting the interpupillary distance from the X-ray tube shift and dividing the remainder by two. It will. be observed that the visual axes of the two eyes E intersect at a point whose distance from the eyes is denoted by IK.. In the illustration under consideration this distance IK is equal to 15 inches, which was assumed as the normal viewing distance. Although this arrangement fulfills the convergence requirement, it does not provide precise, comfortable stereoscopy since accommodation andconvergence do not harmonize, as the eyes are attempting to accommodate for Hinches and atthe same time to converge for '15 'inches.

In order to provide for harmony of accommodation and convergence, I position a nega-' tive lens 14, 15 before each eye E, E as clearlyshown in Fig. 3. These lenses are so chosen that they will image the films 11 and 12 at a plane which is located at normal f viewing distance from the eyes, in this case 15 inches. Hence, the convergence and accommodation are harmonized as the eyes are both accommodating and converging for a distance of 15 inches. The lenses 14, 15 will be comparatively weak, say about 2 dioptres, and since they are placed close to the nodal points of the eyes, tended by the images formed by these lenses will be equal, within the limits of negligible amount, to those subtended by the films when viewed without lenses. The arrangement of Fig. 3, therefore, illustrates a correct method of viewing, according to my invention, stereograms which are small enough to be entirely separated by the oifset introduced as hereinbefore explained. 4 1 1 .As will often be the case, the films or stereograms will be of a comparatively large size, say 14 by 17 inches for offset illustrated in Fig. 2 will not completely separate the films. Since it is essential that each eye sees its respective 'stereogram, re-

course must be had to the reflecting type of A being produced with the source in dotted line position at the left in Fig. 1. As clearly illusand 12 are positioned laterally with respect to the viewing device. My improved viewing device comprises two angularly disposed reflectors M, M which the images of the two films or stereograms 11. 12'. Cooperating example, so that the the angles subwith these mirrors are-the negative lenses 14d 15 whereby the reflected images are image atja plane PL which is located at normal viewing distance in front of the eyes E, E of the observer. The reflectors M, M" are positioned so that each lies at an angle of substantially 45 degreesto the axis 00, each reflector being perpendicular to the plane which is defined by the two positions of the X+raysource and the center of the film, as shown in Fig. 2', and so that this plane pierces the reflectors at mid-height.

The axis 00 is imaged normally to itself and extends to the right and left as shown by two. The optical paths rom the eyes to the mirrors and thence to the films are shown in full lines in Fig. 4, the positions of the images behind the mirrors being shown in dotted lines.

In order to obtain precise and comfortable stereosco ic viewsin accordance with my invention, it is essential that the optical path from the eye to the reflector and thence to the film should be equal to the exposure distance. As indicated on Fig. 4, the distance X L plus the distance Y equals the exposure distance CD. Although I have shown two plane reflectors M and M, it is obvious that other reflecting means, such as prisms, may also be used. If prisms are used for reflectors, the

' glass path of the prisms must be reduced to air path in determining the distances at which the films are located.

With the arrangement illustrated in Fig. 4, precise and comfortable stereoscopic views may be obtained in accordance with my invention, as the eyes E, E are both accom-' modating and converging for the image plane PL which is positioned at normal viewing distance in front of the eyes of the observer. The conver ence angle, which is the angle formed by t e intersecting visual axes of the two eyes, is indicated at W.

In order to obtain precise and comfortable stereoscopic views, it is essential that the various distances and locations, hereinbefore described, :be strictly observed. I In other 7 words, a pair of films taken under the assumed specific conditions as to convergence and exposure distance, must be located in the stereo-. scope in only one position with respect to. the optical axes of the stereoscope and of the exposure apparatus in order that they may be viewed under these specific convergence conditions. This precise location of films can be effected by using suitably arranged indicia means. Such means may take the form of a pair of points made of material which is opaque to X -rays and located on the film holder or casette, whereby a trace of these marks will be madeon-the exposed films. A pair of properly arranged marks are arranged on the film holders of the-viewing device so that the films (willbe properly located when the markson the films are placed in register with themarks on the viewing device.

It is to be understood that the films or stereograms to be viewed-are placed in front of the usual illuminated viewing boxes as are well known to one skilled in the art. My invention is not limited to the use of a normal viewing distance of 15 inches and an exposure distance of 45 inches, as these specific figures are by way of illustration only and it is obvious that my invention can be equally well applied to other viewing and exposing distances. It is also obvious that various modifications can be made without departing from the spirit of my invention and the specifications and accompanying drawings are to be interpreted as illustrative only and not in any limiting sense.

From the foregoing it will be apparent that I am able to attain the objects of my'invention and provide an improved viewing device for stereoscopically recomposing stereograms which have been taken under geometrically homologous conditions.

I claim: p v

1. A device for stereoscopically recompos ing X-ray stereograms comprising angularly disposed reflecting means for reflecting ima es of stereograms which are disposed latera ly of said reflecting means at a predetermined distance and optical means associated with said reflecting means for forming said reflected images at a distance from the observer which is less than the predetermined distance between the stereograms and the reflecting means.

. 2. A stereoscope comprising angularly disposed reflecting means for reflectin images of'objects positioned laterally of said means at a predetermined distance, and light diverging elements positioned in front of said reflecting means and in the paths of reflectors whereby the reflected images are formed at a distance from the observer which is less than thedista-nce between the object and said reflecting means.

3. A stereoscope for viewing two spaced stereograms comprising two angularly disposed reflectors, said reflectors being positioned and adapted to reflect, respectively, images of saidstereograms, and negative lens means located opposite each of said reflectors and positioned in the paths of reflection whereby the reflected images when viewed through said lens means are formed at normal viewing distance.

'4. A stereoscope for viewing two spaced parallel stereograms comprising two reflectors positioned between said stereograms, the

planes of said reflectors making angles of substantially. forty-five degrees with the planes of said stereograms, negative lens means positioned opposite each of said reflectors and in the paths of reflection, said lenses being constructed so that upon looking through them an observer will see images of said stereograms at normal viewing distance.

5. A stereoscope for recomposing stereograms which are located in spaced parallel planes comprising two contacting angularly disposed reflectors which are positioned between said planes, said reflectors being positioned to rearwardly reflect, respectively, images of said stereograms, the center of each of said stereograms being offset a predetermined distance from said reflectors and a negative lens positioned opposite each of said reflectors in the path of reflection, said negative lenses being constructed so that upon looking therethrough an observer will see reflected images of said stereograms positioned at normal viewing distance. 

